The present disclosure relates to a brake device having an actuator, which is operated by a pressure medium, for the application and release of a vehicle brake, particularly of a rail vehicle brake.
From the state of the art, brake devices having pressure-medium-operated actuators are known where the brake is applied by the controlling of a pressure medium, such as compressed air, into the brake cylinder. This type of an active brake cylinder is used, for example, for the service brake of rail vehicles. Furthermore, pressure-medium-operated actuators with passive brake cylinders are known, where the application of the brake takes place by spring tension and the brake is released by the applying a pressure medium into the brake cylinder. Thus, despite a loss of pressure medium, such brakes are operable in the application direction and are used, for example, for parking or emergency brake devices of rail vehicles.
In the case of a brake device of this type according to European Patent Document EP-A-1 086 867, one of two pressure chambers separated by a piston is pressurized for the application of the brake. When the brake is released, the compressed air in the pressurized pressure chamber promotes the release operation in that it is guided by an actuator into the other chamber which is constantly connected with the atmosphere by a discharge which cannot be controlled. A pressure head therefore forms in the other pressure chamber which promotes a release of the brake. As a result of the overflowing of the compressed air, the latter is used several times and no longer has to be produced by the pressure medium source. In addition, the braking torque can rapidly be lowered in the event of a breakdown of the rotational wheel speed.
U.S. Pat. No. 4,575,159 describes a rail vehicle brake system having a cylinder piston drive in the case of which the piston is spring-loaded in the brake application position. Both sides of the piston can be acted upon by pressure medium by means of a control device which utilizes a pressure difference between the piston surfaces for the service brake.
In contrast, the present disclosure is based on the object of further developing a brake device of the initially mentioned type such that it has a still lower pressure medium consumption as well as a still faster reaction to braking and deceleration demands.
In the present disclosure, instead of releasing pressure medium into the environment for the reduction of pressure in the pressure chambers, a portion of the pressure medium present in the respective pressure chamber acted upon by pressure is guided into the other pressure chamber by opening an overflow valve and is utilized there for the pressure buildup. Pressure medium is therefore utilized several times and no longer has to be generated by the pressure medium source. This results in a lower pressure medium consumption of the pressure-medium-operated actuator and therefore in a pressure medium supply with smaller dimensions, particularly in smaller storage air tanks. As an alternative, while the dimensioning of the pressure medium supply is not changed, the size of the brake cylinder can be reduced in order to generate a defined braking or releasing force. This is because a portion of the braking or releasing force is generated already by the amount of pressure medium flowing over from one pressure chamber into the other pressure chamber. This is advantageous particularly when the actuator is used in low-floor short-distance vehicles, in the case of which a limited amount of space is available for the brake cylinders. Furthermore, the valve cross-sections of the ventilation valves and bleeder valves can be reduced because only a portion of the pressure medium required for the application and for the release of the brake respectively still flows through them.
Since the overflow valve now also acts during the transition phase between the release position and the application position, the overflowing pressure medium promotes the application operation, which results in a faster reaction to a braking demand. In comparison to European Patent Document EP-A-1 086 867, which utilizes overflowing medium only during the brake release phase, this pressure medium is not immediately discharged but remains in the pressure chamber until a pressure balance occurs, so that the pressure energy present in the pressure medium is optimally utilized. The ventilation and bleeder valves provide a further increase or decrease of the pressure level adjusted by the overflowing.
According to a particularly preferred embodiment of the invention, the adjusting piston is spring-loaded in the direction of the application position. This will result in an initially described passive brake cylinder. The pressure balancing valve is preferably opened until a fraction of a maximally reachable braking force or releasing force has been generated. The maximal force is then achieved by an additional ventilating and bleeding of the respective pressure chambers.
Preferably, ventilation and bleeder valves are provided for the ventilating and bleeding of the two pressure chambers, which are closed during the opening time of the overflow valve, a pressure buildup or pressure reduction taking place by the opening or closing of the ventilation or bleeder valves which exceeds the pressure balance in the two pressure chambers.